Joins

A JOIN clause is used to combine rows from two or more tables in a database, based on a column that is common to them.

INNER JOIN

An inner join returns records that have identical values in both the tables.

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SELECT Orders.OrderID, Customers.CustomerName
FROM Orders

INNER JOIN Customers ON Orders.CustomerID = Customers.CustomerID;

The below query will help perform an inner join on three tables.

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SELECT Orders.OrderID, Customers.CustomerName, Shippe rs.ShipperName
FROM ((Orders
INNER JOIN Customers ON Orders.CustomerID = Customers.CustomerID)
INNER JOIN Shippers ON Orders.ShipperID = Shippers.ShipperID);

LEFT OUTER JOIN

A left inner join returns all the records from the left-sided table, and the matching records from the right-sided table.

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SELECT Customers.CustomerName, Orders.OrderID
FROM Customers
LEFT JOIN Orders ON Customers.CustomerID = Orders.CustomerID
ORDER BY Customers.CustomerName;

RIGHT OUTER JOIN

A right inner join returns all records from the right-sided table, and the matching records from the left table.

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SELECT Orders.OrderID, Employees.LastName, Employees.FirstName
FROM Orders
RIGHT JOIN Employees ON Orders.EmployeeID = Employees.EmployeeID
ORDER BY Orders.OrderID;

FULL OUTER JOIN

A full outer join returns all records from both tables when there is a match in either the left-sided or the right-sided table.

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SELECT Customers.CustomerName, Orders.OrderID
FROM Customers
FULL OUTER JOIN Orders ON Customers.CustomerID=Orders.CustomerID
ORDER BY Customers.CustomerName;